The use and implementation of computer networks has become very popular. Networks such as Local area networks (LANs), Metropolitan area networks (MANs), Wireless LANs (WLANs) and the like, are being widely implemented for the purpose of accessing data. The use of such networks has led to the development of various international standards in the field of communication such as WiFi and WiMAX.
WiMAX is a wireless metropolitan area network (MAN) technology that can connect Wi-Fi hotspots with each other and to other parts of the Internet and provide a wireless alternative to cable and DSL. WiMAX provides up to 50 km (31 miles) of linear service area range and allows connectivity between users without a direct line of sight. The technology has been claimed to provide shared data rates up to 70 Mbit/s, which, according to WiMAX proponents, is enough bandwidth to simultaneously support more than 60 businesses and well over a thousand homes at 1 Mbit/s DSL-level connectivity. Real world tests, however, show practical maximum data rates between 500 kbit/s and 2 Mbit/s, depending on conditions at a given site.
Also WiMAX allows interpenetration for broadband service provision of VoIP, video, and Internet access simultaneously. Even in areas without pre-existing physical cable or telephone networks, WiMAX allows access between networks which are within range of each other. WiMAX antennas share a cell tower without compromising the function of cellular arrays already in place. WiMAX antennas may also be connected to an Internet backbone via either a light fiber optics cable or a directional microwave link. WiMAX also facilitates increase in bandwidth for a variety of data-intensive applications.
WiMAX has become synonymous with the IEEE 802.16 standard family, an emerging standard for fixed and mobile MAN (Metropolitan Area Network) Broadband Wireless Access (BWA). The original 802.16 and the subsequently amended 802.16a standards are both used for fixed BWA. The latter caters for non-line of sight (NLOS) applications, as BWA is increasingly becoming a residential application. The latest 802.16e amendment is supporting for mobility (mobility at vehicular speeds, around 120 km/h) in WiMAX system. The 802.16e standard will allow users' hardware (notebooks, personal digital assistants (PDAs)) to access high speed Internet, and while roaming outside of the WiFi (Wireless Fidelity) hotspots. The 802.16 standard supports high data rates (up to about 70 Mbps) with a variety of channel coding options. The mandatory scheme is a convolutional code. Convolutional turbo codes, turbo product codes and LDPC codes are optional. These optional codes can be used to ensure robustness in extreme fading channels.
LDPC codes are linear block codes originally proposed by Gallager in the early 1960s. Their parity check matrix is sparse and has low density of one's. The original codes were regular codes having uniform column and row weight in the parity check matrix. Recently, these codes have emerged as competitors for turbo codes, with capacity approaching performance. Better performance of LDPC codes is achieved with a proper choice of code and decoding signal processing. A popular LDPC decoding algorithm is the Belief Propagation algorithm also referred to as Sum-Product algorithm. The Sum-product algorithm is a message passing algorithm operating on the Tanner graph, which is a bipartite graph representing the parity check matrix and consisting of variable nodes and check nodes. A bipartite graph is a special graph where the set of vertices can be divided into two disjoint sets with two vertices of the same set never sharing an edge.